1. Field of the Invention
The invention relates to fluorophores and more particularly to highly fluorescent and analyte sensitive boronic acid containing fluorophores and for methods of using same for measuring analyte concentrations, such as glucose in physiological fluids, such as the blood and tears, in a continuous and non-invasive manner. The invention further relates to ophthalmic devices comprising the fluorophores, which interact with the analyte to be measured providing an optical signal being indicative of the analyte level in an ocular fluid.
2. Background of the Related Art
Individuals suffering from diabetes mellitus have an abnormally high blood sugar level, generally because the pancreas does not secrete sufficient amounts of the active hormone insulin into the bloodstream to regulate carbohydrate metabolism. If an abnormally high blood sugar level, known as a hyperglycemic condition, is allowed to continue for prolonged periods, the individual will suffer from the chronic complications of diabetes, including retinopathy, nephropathy, neuropathy and cardiovascular disease. Presently, approximately 150 million people worldwide are affected by diabetes. Studies indicate that diabetic patients who are able to maintain near normal glycemic control greatly reduce the likelihood of these direct complications. Therefore, several tests have been developed to measure and control the glycemic condition.
One common medical test to control glycemic condition is the direct measurement of blood glucose levels. Blood glucose levels fluctuate significantly throughout a given day, being influenced by diet, activity, and treatment. Depending on the nature and severity of the individual case, some patients must measure their blood glucose levels up to seven times a day. Methods of glucose analysis include electrochemistry, near infrared spectroscopy, optical rotation, colorimetry, fluorimetry, and the enzyme-based method, the latter being the most commonly used. Unfortunately, the enzyme-based method has several disadvantages, including the requirement of “finger pricking,” which is highly invasive and often inconvenient. It is known that many diabetic patients often skip the analysis step, i.e., drawing blood, and administer an estimated dose of insulin, which can lead to substantial fluctuations in insulin levels over time. Further, the enzyme-based method is not continuous, thus putting the patient at risk of unacceptably high or low glucose levels.
In recent years, various non-invasive and minimally-invasive technologies have been proposed in the academic and patent literature to monitor glucose levels in the blood, ocular fluid, e.g., tears, aqueous humor or interstitial fluid. For example, the GlucoWatch® non-invasively monitors glucose levels in the interstitial fluid every ten minutes for up to thirteen hours. However, the GlucoWatch® manufacturers expressly state that the GlucoWatch® is designed to merely supplement conventional blood glucose monitoring.
U.S. Pat. No. 6,681,127 discloses an ophthalmic lens, including a chemical sensor, to determine the amount of an analyte, e.g., glucose, in an ocular fluid. Such ophthalmic lens includes a receptor moiety, which can bind either a specific analyte, e.g., glucose, or a detectably labeled competitor moiety. The amount of detectably labeled competitor moiety which is displaced from the receptor moiety by the analyte is measured and provides a means of determining analyte concentration in the ocular fluid. A disadvantage of this method includes the potential that other compounds are present in the fluid that are capable of displacing the competitor moiety, thereby giving a false analyte concentration.
It is well known in the glucose monitoring arts that tear glucose levels directly track blood glucose levels, however, the concentration of glucose in tears, e.g., 50-500 μM, is about ten times lower than the corresponding blood glucose level (Van Haeringen, N. J., Surv. Ophthalmol., 29(2), 84-96 (1981); Gasser, A. R., et al., Am. J. Ophthalmol., 65(3), 414-420 (1968); Das, B. N., et al., J. Indian Med. Assoc., 93(4), 127-128 (1995); Chen, R., et al., J. Capillary Electrophor., 3(5), 243-248 (1996); Perez, S. A., Electrophoresis, 17(2), 352-358 (1996); Jin, Z., Anal. Chem., 69(7), 1326-1331 (1997)). Accordingly, to determine the concentration of glucose in tears requires a methodology that is highly sensitive relative to standard blood glucose methods. To date, attempts to monitor tear glucose concentrations have been invasive and applied non-continuous methodologies.
Therefore, there is a continuing need for new methods of determination of monosaccharide, e.g., glucose and fructose that are sensitive enough to quantitatively determine monosaccharide levels in tears and other bodily fluids under physiological conditions. These methods should be continuous, non-invasive and uncomplicated, thereby ensuring the diabetic actively monitors their blood glucose levels.
Correspondingly, there is a need for methods of determination of levels of a variety of other analytes in tears and other bodily fluids under physiological conditions, for applications including monitoring of patient stability, medication compliance, exposure of individuals to environmental contaminants and toxins, etc.